Submicron Porous Gradient TPU/MWCNT Foam with Electromagnetic Shielding Performance

The widespread use of electronic products has led to serious electromagnetic pollution, which poses potential threats to communication systems and human health. The electromagnetic shielding effect can be significantly improved by increasing the conductivity of electromagnetic shielding materials, but impedance mismatch effects and serious secondary pollution are inevitable. Based on the nonsolvent-induced phase separation method, a gradient submicrometer porous structure sample was developed in this paper. Its continuous gradient conductive porous structure effectively improved excessive electromagnetic wave reflection pollution and the impedance mismatch effect. The thermoplastic polyurethane (TPU) and multiwalled carbon nanotube (MWCNT) blend solutions with different contents of MWCNT were deposited on the surface of the porous TPU/MWCNT material and induced in situ phase transformation repeatedly, and a multilayer porous material with gradient conductivity and a microcell structure was prepared. The cell size of the prepared TPU/MWCNT porous material is around 4 μm, which is much smaller than the size range of the existing electromagnetic shielding porous materials. The multilayer TPU/MWCNT porous materials effectively alleviate the impedance mismatch between the materials and the surrounding environment. The values of the total shielding effectiveness (SET) of the multilayer porous materials have reached over 24 dB, and the values of the reflective shielding effectiveness (SER) are less than 3 dB. The tensile test results show that the mechanical properties of the three-layer porous material present typical isotropic elastic polymer characteristics. The stress–strain curve is similar to that of the single-layer TPU/MWCNT porous material, and the tensile fracture section proves the stability of the bonding between the layers of the porous material. Moreover, the materials showed excellent flexibility performance in tensile, bending, and twisting tests. Therefore, the results of this study will have prospects in the application of flexible and high-performance electromagnetic shielding porous composite materials.